The present invention is directed generally to a release agent delivery system for use in an electrophotographic printing process. More particularly, the present invention is directed to the use of a non-woven textile web for use as a release agent delivery device in a release agent delivery system. Most specifically, the present invention is directed to the use of a non-woven thermally bonded textile web of essentially sub-denier fibers in a release agent delivery system. The use of the textile web of sub-denier fibers provides very fine release agent flow patterns that yield highly improved print quality through decreased microscopic streaking of the release agent.
In the process of electrostatic printing, a latent electrostatic image is recorded on a photosensitive member with subsequent rendering of the image visible by the application of electrostatic marking particles, typically referred to as toner. The visual image formed by the toner particles is then transferred from the photosensitive member to a sheet of paper with subsequent affixing of the toner particles onto the paper.
To fix or fuse the toner particles onto the paper permanently by heat, the temperature of the toner particles is elevated to a point at which the constituents of the toner coalesce and become tacky. This causes the toner to flow to some extent into the fibers or pores of the paper. As the toner cools, solidification of the toner occurs, causing the toner to be bonded firmly to the paper.
One method of thermally fusing toner particles onto the paper is to pass the paper, with the unfused toner particles thereon, between a pair of opposed roller members, at least one of which is internally heated. During the operation of a fuser system of this type, the paper to which the toner particles has been electrostatically adhered, is moved through the nip formed between two rolls with the toner particles contacting the heated user roll to thereby effect heating of the toner particles within the nip. Typically these fuser systems contain two rolls, the fuser roll and the compression roll. The fuser roll is typically coated with a compliant material, such as silicone rubber, low surface energy elastomers, or polytetrafluoroethylene (PTFE) resin sold by E. I. DuPont De Nemours under the trademark TEFLON. One drawback of these prior art fuser systems is that since the toner particles are tackified by heat, part of the particles forming the image carried on the paper are often retained by the heated fuser roller rather than penetrating the paper""s surface. This tackified toner often sticks to the surface of the fuser roller and then gets deposited onto the following paper or onto the mating pressure roller. This depositing of toner onto the following paper is known as xe2x80x9coffsettingxe2x80x9d. Offsetting is an undesirable occurrence which lowers the sharpness and quality of the immediate print as well as contaminating the following prints with toner.
To alleviate the toner offsetting problem, it is common practice to utilize release agents, such as silicone oils which are applied to the fuser roll surface to act as a toner release material. These toner release agents possess a relatively low surface energy and are suitable for use in the heated fuser roll environment. In practice, a thin layer of silicone oil is applied to the surface of the heated fuser roll to form an interface between the fuser roll surface and the toner particles carried on the support material or paper. Thus, a low surface energy, easily parted layer is presented to the toners that pass through the fuser nip and thereby prevents toner from adhering to the fuser roll surface.
Numerous systems have been used to deliver toner release agents, such as silicone to the fuser roll. These systems typically incorporate a textile as the release agent fluid or oil holding and delivery medium. These textiles also serve a critical roll in that they are utilized as a fuser roller cleaning mechanism. With each rotation of the fuser roller, there may be some non-released toner particles remaining on the surface of the fuser roller. These non-released toner particles are then captured in the interstices of the textile fibers as the textile moves relative to the rotating fuser roller.
One of the more commonly used textiles in electrophotographic printing machines is known as a thermal bonded non-woven textile. Other textiles include those known as spun bond non-wovens and hydroentangled non-wovens. Many of the textiles used in electrophotographic printing machines are typically made with some content of polyester fibers and Aramid fibers. These textiles are also sometimes made of Imide, polyphenylene sulfide (PPS), PTFE, and viscose rayon fibers. The textiles are typically impregnated with a silicone oil such as those sold by the Dow Corning Corporation. Many of these silicone oil impregnated textiles are manufactured at BMP America Incorporated located in Medina, N.Y. and Portland, Oreg., or at BMP Europe Limited located in Accrington, Lancashire, United Kingdom.
Although these oil impregnated textiles meet most application requirements, some applications demand improved image quality. In an effort directed to having an electrophotographic print approach the image quality of a traditional silver halide developed photograph, every step towards improved electrophotographic print quality is critical in today""s market. Certain image or print quality issues still exist with the presently used textile materials. Under most conditions, current textile materials create silicone oil flow patterns on the fuser roller, which oil flow patterns correspond to high, low, and void areas of the textile""s fibers. These oil flow patterns are circurnferentially positioned on the fuser roller""s surface with high oil flow patterns corresponding to the textile""s fiber void regions and with low oil flow patterns corresponding to the textile""s high fiber regions. These microscopic oil streaks get transferred to the printed page thereby creating microscopic image variations. These microscopic image variations are in the form of alternating lines of gloss and matte finish. An image""s appearance is created by the combination of substrate type, i.e. paper, transparency, card stock, toner type, printing process, and oil quantity. Pages printed with heavy oil appear to have a glossy finish, pages printed with light oil appear to have a matte finish, and pages printed with non-uniform oil appear to have a non-integrated finish, the result of alternating glossy and matte finish areas. These non-uniformity finishes are very undesirable in printed pages. As these non-uniform finish areas become smaller, they become more difficult to notice. Every step towards decreasing their size is a step towards improving print quality.
It is an object of the present invention to provide a release agent delivery system for use in an electrophotographic printer.
Another object of the present invention is to provide a non-woven textile fabric web useable as a release agent delivery device.
A further object of the present invention is to provide a non-woven thermally bonded textile web of essentially sub-denier fibers useable as a release agent delivery device.
Still another object of the present invention is to provide a release agent delivery web which will reduce non-uniform finishes on printed pages.
Yet a further object of the present invention is to provide a release agent delivery system which yields a finer, more uniform circumferential release agent pattern on the fuser roller of an electrophotographic printer.
In accordance with the present invention, the release agent is delivered to the fuser roller by a non-woven thermally bonded textile web of essentially sub-denier fibers. These sub-denier fibers provide much improved uniformity of the release agent delivered to the surface of the fuser roller. Instead of alternating visible areas of matte and glossy finish on the print, the deliver of the release agent by the non-woven essentially sub-denier finish textile web in accordance with the present invention results in a much more uniform pattern of release agent delivery to the fuser roller. This more uniform release agent delivery pattern results in a much more uniform finish of the resultant print.
The sub-denier fibers of the non-woven textile web used in the present invention provide a textile with a finer topographical surface. The textile""s surface drags on the fuser roll surface in an oil filled environment. The textile""s finer topographical surface yields a finer circumferential oil pattern, or a pattern with a thinner band width, on the fuser roll surface. As the toner is being fused onto the page, the oil residing on the fuser roller is absorbed into the page. The textile web used in the present invention allows for a much finer pattern of oil, with a much thinner band width, to be absorbed into the page.
Finer width and thus more uniform oil patterns absorbed into the printed page dramatically increase the printed image quality by decreasing the individual bar width of the alternating gloss/matte/gloss/matte regions on the printed page. The decrease in size of the individual bar widths of alternating gloss/matte/gloss/matte regions leads to a more integrated appearance on the printed page. The effects of the present invention are most visibly noticeable in full color prints. These improvements are especially important in the ever quickening race toward achieving traditional photographic or silver halide quality in an electrophotographic print.
In attaining these objectives the present invention utilizes, in one embodiment, a textile web of substantially sub-denier fibers with the web weighing in the range of 10 to 150 grams/square meter and being comprised of greater than 50% fibers which are sub-denier in size. The textile web may be produced by thermal bonding, spun bonding, needle felting, melt blowing, or hydroentanging. The textile is impregnated with release agent which is typically silicone oil to a level of 2.5 to 250 grams/square meter. The resultant release agent delivery system provides greatly improved print quality as a result of the significantly improved uniformity of the toner release agent flow pattern applied to the fuser roller. The present invention is a substantial advance in the art.